Multistage centrifugal pump

Abstract

A multistage pump for conveying a fluid includes an outer pump housing, at least first and last stages arranged in the outer pump housing. Each stage includes a stage casing, an impeller, and a diffuser. A pump inlet supplies the fluid to the impeller of the first stage and, a pump outlet discharges the fluid. Each impeller is mounted to a pump shaft in a torque proof manner, and the impellers are arranged one after another on the pump shaft. The last stage includes a collector with a collector chamber to receive the fluid from the diffuser of the last stage. The first stage includes guide channels to receive the fluid from a diffusor and to guide the fluid to the impeller of the next stage. The collector chamber is displaced in the axial direction with respect to the diffusor of the last stage.

What is claimed: 
     
         1 . A multistage pump for conveying a fluid, comprising:
 an outer pump housing;   a plurality of stages arranged in the outer pump housing, the plurality of stages comprising at least a first stage and a last stage, each of the first stage and the last stage comprising a stage casing, an impeller configured to act on the fluid, and a diffuser configured to surround the impeller and to receive the fluid from the impeller;   a pump inlet configured to supply the fluid to the impeller of the first stage;   a pump outlet configured to discharge the fluid; and   a pump shaft configured to rotate about an axial direction,   each impeller of the first stage and the last stage mounted to the pump shaft in a torque proof manner, the impeller for the first stage and impeller for the last stage arranged one after another on the pump shaft, the last stage comprises a collector with a collector chamber configured to receive the fluid from the diffuser of the last stage, and the first stage comprises guide channels configured to receive the fluid from the diffusor of the first stage and to guide the fluid to the impeller of a next stage, the collector chamber being displaced in the axial direction with respect to the diffusor of the last stage.   
     
     
         2 . The multistage pump in accordance with  claim 1 , wherein the collector chamber is displaced in axial direction with respect to the diffuser of the last stage to such an amount that the diffuser of the last stage and the collection chamber do not overlap in the axial direction. 
     
     
         3 . The multistage pump in accordance with  claim 1 , wherein each impeller of the first stage and the last stage is a radial impeller configured to discharge the fluid in a radial direction with the radial direction being perpendicular to the axial direction. 
     
     
         4 . The multistage pump in accordance with  claim 1 , wherein the collector forms the stage casing of the last stage. 
     
     
         5 . The multistage pump in accordance with  claim 1 , wherein the diffusor of the last stage and the collector are configured such that the fluid is diverted in a radial direction within the collector chamber with the radial direction being perpendicular to the axial direction. 
     
     
         6 . The multistage pump in accordance with  claim 1 , wherein the collector chamber is an annular collector chamber, and an outer diameter of the collector chamber is at most as large as an outer diameter of the diffusor of the last stage. 
     
     
         7 . The multistage pump in accordance with  claim 6 , wherein the outer diameter of the collector chamber is equal to the outer diameter of the diffusor of the last stage. 
     
     
         8 . The multistage pump in accordance with  claim 1 , wherein the plurality of stages comprises at least one intermediate stage, and wherein the at least one intermediate stage is arranged between the first stage and the last stage. 
     
     
         9 . The multistage pump in accordance with  claim 1 , comprising a plurality of tie rods configured to fix the plurality of stages with respect to each other, each tie rod extends in the axial direction parallel to the pump shaft through the plurality of stage casings. 
     
     
         10 . The multistage pump in accordance with  claim 1 , wherein the outer pump housing comprises a barrel casing, which is configured the plurality of stages, so that the barrel casing encloses the plurality of stages. 
     
     
         11 . The multistage pump in accordance with  claim 10 , wherein the barrel casing has a tubular shape and extends from a first axial end coaxially with the pump shaft to a second axial end. 
     
     
         12 . The multistage pump in accordance with  claim 11 , further comprising a suction cover configured to close the first axial end of the barrel casing, and a discharge cover to close the second axial end of the barrel casing. 
     
     
         13 . The multistage pump in accordance with  claim 12 , wherein each of the suction cover and the discharge cover is secured to the barrel casing by fixing elements.